Summary of the invention
The purpose of this invention is to provide a kind of comparatively accurately to short leading method of carrying out synchronously with the original position of determining long preambles.
For achieving the above object, the technical solution used in the present invention is:
A kind of method for synchronous for the MIMO-OFDM system is applied in the MIMO-OFDM system to carry out slightly synchronously to determine the original position of long preambles to the weak point of OFDM frame is leading, and it comprises the steps:
(1) by selecting valid data in the data that receive, described valid data are lacked lead data for each reception antenna in the part of finishing after energy measuring is determined to receive frame data;
(2) described valid data are postponed auto-correlation computation and computing cross-correlation, obtain auto-correlation computation result and computing cross-correlation result;
(3) to described auto-correlation computation result slide difference and running integral computing and find out the maximum of points of operation result;
(4) determine the scope that exists of cross-correlation peak value according to described maximum of points;
(5) at the peak value of seeking the computing cross-correlation result in the scope that exists of described cross-correlation peak value, determine the original position of described long preambles.
Preferably, in the described step (1), described valid data are the short lead data of the time domain after the energy measuring.
Preferably, in the described step (2), the delay length of described delay auto-correlation computation is the leading one-period of described weak point.
Preferably, in the described step (2), the described valid data that each reception antenna is received carry out auto-correlation computation and result's summation are obtained described auto-correlation computation result; The sequence that described valid data and the weak point that passes through channel is leading is not carried out the described computing cross-correlation result that computing cross-correlation obtains each reception antenna.
Preferably, in the described step (3), the length of the employed sliding window of described slip difference and described running integral is the leading half period length of described weak point.
Preferably, in the described step (3), described auto-correlation computation result is carried out multi-form slip calculus of differences twice, and respectively the result of twice slip calculus of differences is carried out the running integral computing, find out the maximum of points among the result of twice running integral computing respectively, be respectively first maximum of points and second maximum of points.
Preferably, in the described step (4), find out the theoretical position of described maximum of points respectively, calculate the distance between the starting point of the starting point of the leading one-period of the weak point at this maximum of points and its place and short leading next cycle, the theoretical original position of the one-period that the weak point that obtains this maximum of points place according to above-mentioned two distances is leading and short leading next cycle; A given radius, the theoretical original position with the leading cycle of above-mentioned two weak points is the center of circle respectively, the interval in the scope of described radius is the scope that exists of described cross-correlation peak value.
Preferably, in the described step (5), in described computing cross-correlation result, find out several peak values, if all have at least one described peak value in the scope in the existing of each described cross-correlation peak value of described first maximum of points, then the position of Zui Da described peak value is the described weak point at this peak value place accurate original position in leading cycle, also is the original position of described long preambles; If all have at least one described peak value in the scope in the existing of each described cross-correlation peak value of described second maximum of points, then the position of Zui Da described peak value is the described weak point at this peak value place accurate original position in leading cycle, also is the original position of described long preambles; If all can not find described peak value in the existing in the scope of described cross-correlation peak value of described first maximum of points and described second maximum of points, then the position of described first maximum of points is the original position of described long preambles.
Because technique scheme is used, the present invention compared with prior art has following advantage: method for synchronous of the present invention, consider a problem from actual, and utilized the position of auto-correlation and cross correlation results to concern and the periodicity of cross-correlation peak value and the statistical property under the noise effect, has the higher synchronous precision, it not only can be applied on the 802.11n, all can use other similar MIMO-OFDM systems with targeting sequencing, has wideer range of application.
Embodiment
Be further described below in conjunction with the present invention of embodiment shown in the drawings.
Embodiment one: a kind of method for synchronous for the MIMO-OFDM system, be applied to carry out slightly synchronously to determine the original position of long preambles the weak point of OFDM frame is leading in the MIMO-OFDM system, HT-MIXED FORMAT PPDU with 802.11n is example, when receiving terminal need be estimated to received signal synchronously, detect as follows according to the flow process shown in the accompanying drawing 2.
The first step is by selecting valid data in the data that receive.These valid data are lacked lead data for each reception antenna in the part of finishing after energy measuring is determined to receive frame data.In this example, select relatively harsher situation, have only 3 short symbol periods after namely frame detects.As shown in Figure 3, namely have only 3 L-STS.In this step, valid data are the short lead data of the time domain after the energy measuring.
Second step postponed auto-correlation computation and computing cross-correlation to valid data, obtained auto-correlation computation result and computing cross-correlation result.
Specifically, the delay length of delay auto-correlation computation is short leading one-period.The valid data that each reception antenna is received carry out auto-correlation computation and result's summation are obtained the auto-correlation computation result; The sequence that valid data and the weak point that passes through channel is leading is not carried out the computing cross-correlation result that computing cross-correlation obtains each reception antenna.
For example, note r
j(k) be k the sampled data that j reception antenna receives.Auto-correlation computation is:
Wherein Ls is the length in short leading each cycle, and the result of calculation addition of each antenna is obtained
Be the auto-correlation computation result, wherein N
RBe the reception antenna number.λ in result such as the accompanying drawing 3
aShown in.Computing cross-correlation is:
S wherein
i(m) be original short targeting signal.Cross-cor is the computing cross-correlation result of certain two reception antenna in the accompanying drawing 3.
The 3rd step is to auto-correlation computation result slide difference and running integral computing and find out the maximum of points of operation result.
The auto-correlation computation result is carried out multi-form slip calculus of differences twice, and respectively the result of twice slip calculus of differences is carried out the running integral computing, the length of the employed sliding window of slip difference and running integral is short leading half period length.Find out the maximum of points among the result of twice running integral computing respectively, be respectively first maximum of points and second maximum of points.
Getting sliding window length is L
w=L
s/ 2, and according to formula
Carry out first kind of slip difference, as Ω in the accompanying drawing 3
1Shown in.The slip difference result is carried out running integral, as shown in the formula:
As S in the accompanying drawing 3
1Shown in.Find out S
1Middle maximum is first maximum of points.Carry out second kind of slip difference then,
As Ω in the accompanying drawing 3
2Shown in.This slip difference result is carried out running integral:
As S among Fig. 3
2Shown in.Find out S
2Middle maximum is as second maximum of points.Above-mentioned two maximum of points all mark with rhombus in accompanying drawing 3.
The 4th goes on foot, and determines the scope that exists of cross-correlation peak value according to maximum of points.Find out the theoretical position of first maximum of points and second maximum of points respectively, calculate respectively this two and the starting point of the starting point of the leading one-period of the weak point at its place and short leading next cycle between distance, the theoretical original position of the one-period that the weak point that obtains this maximum of points place according to above-mentioned two distances is leading and short leading next cycle.For example, the position of first maximum of points obtains receiving the initial point position in short leading the 9th cycle of signal and the tenth cycle respectively according to this in the centre position in short leading the 9th cycle in theory, is respectively M
9,1And M
10,1The position of second maximum of points after short leading the 9th cycle starting point four/one-period the place.Obtain the initial point position in short leading the 9th cycle and the tenth cycle according to this respectively, be respectively M
9,2And M
10,2
A given radius R again, the theoretical original position with the leading cycle of above-mentioned two weak points is the center of circle respectively, the interval in the scope of radius is the scope that exists of cross-correlation peak value, namely obtains two interval [M of first maximum of points
9,1-R, M
9,1+ R] and [M
10,1-R, M
10,1+ R], and two interval [M of second maximum of points
9,2-R, M
9,2+ R] and [M
10,2-R, M
10,2+ R].
In the 5th step, at the peak value of seeking the computing cross-correlation result in the scope that exists of cross-correlation peak value, determine the original position of long preambles.
By finding out N peak value among the computing cross-correlation result, get its position and form set G.If all have at least one peak value in the scope in the existing of each cross-correlation peak value of first maximum of points, namely there is the element among at least one G, then the position of largest peaks is the weak point at this peak value place accurate original position in leading cycle, also is the original position of long preambles.If all have at least one peak value in the scope in the existing of each cross-correlation peak value of second maximum of points, namely there is the element among at least one G, then the position of largest peaks is the weak point at this peak value place accurate original position in leading cycle, also is the original position of long preambles.If all can not find peak value in the existing in the scope of cross-correlation peak value of first maximum of points and second maximum of points, then the position of first maximum of points is the original position of long preambles.
Above-mentioned execution mode provides a kind of method for synchronous that has degree of precision in the MIMO-OFDM system, it is can be in amount of available data limited and be subjected to find out in the reception signal of noise jamming the initial point position of long preambles, according to the disclosed embodiments, those skilled in the art can realize or use the present invention.Because the short leading periodicity of this method for synchronous utilization is adjudicated and is obtained final synchronized result, in the TGn standard channel, even data available seldom also has excellent performance, especially be fit to be applied in the long preambles of 802.11n thick synchronously in.
Above-described embodiment only is explanation technical conceive of the present invention and characteristics, and its purpose is to allow the personage who is familiar with this technology can understand content of the present invention and enforcement according to this, can not limit protection scope of the present invention with this.All equivalences that spirit essence is done according to the present invention change or modify, and all should be encompassed within protection scope of the present invention.